There have been recently demanded coating compositions capable of forming coating films having high hardness as well as excellent in weatherability, contamination resistance, and chemical resistance. Hereinafter, high versatility will be also demanded for coating compositions. As such coating compositions, compositions comprising a silyl group-containing vinylic resin and an organosilane compound were proposed in Patent Document 1 (Japanese Patent Laid-open Publication No. H01-69673), Patent Document 2 (Japanese Patent Laid-open Publication No. H01-69674), Patent Document 3 (Japanese Patent Laid-open Publication No. H04-108172), and Patent Document 4 (Japanese Patent Laid-open Publication No. H04-117473). Further improvement is, however, demanded for these coating compositions in terms of adhesion to organic substrates.
There have been recently proposed numerous coating compositions in which a photocatalyst component is blended. Such a photocatalyst-containing coating composition is applied to surfaces of various substrates to form a photocatalytic layer, and its photocatalytic action makes the surface of coating film hydrophilic, whereby the contamination resistance of the substrate (a layered product) is improved. However, for substrates made of organic material such as resin, there has been a problem that the organic material that is a substrate is decomposed by radicals generated through the photocatalytic action of the photocatalytic layer, resulting in degradation of the substrate. For this reason, when the photocatalytic layer is formed on the surface of the organic substrate, an intermediate layer is often formed between the photocatalytic layer and the organic substrate in order to protect the organic substrate.
As an undercoating composition used for such an intermediate layer, there may be mentioned a composition containing polysiloxane and an organic polymer, for example, the composition comprising the organosilane compound and the silyl group-containing vinylic resin. Such a composition that comprises the polysiloxane and the organic polymer is excellent in weatherability and resistance to radicals generated by the photocatalytic action.
There was a problem, however, that increase in the polysiloxane content causes poorer adhesion to organic substrates although the weatherability is improved. Further, there was a problem that increase in the organic polymer content causes poorer weatherability although the adhesion to organic substrates is improved. In addition, since a polysiloxane and an organic polymer were poorly compatible with each other, it was difficult to mix them homogeneously, and the resultant coating film tended to be opaque.
Patent Document 1: Japanese Patent Laid-open Publication No. H01-69673
Patent Document 2: Japanese Patent Laid-open Publication No. H01-69674
Patent Document 3 Japanese Patent Laid-open Publication No. H04-108172
Patent Document 4: Japanese Patent Laid-open Publication No. H04-117473